Joining the 300D club

[lws1]

Well, after posting a lot of dumb questions and learning a lot from you-all, I put a deposit on a 1985 300D. I am really excited (Is it properly known as a 300DT? it's a sedan - I know it's not a 300TD because that's a wagon - but this sedan is a turbo). The car has 130,000 miles and it was the second owner who drove it once a week or just enough and was a DIY'r, so EVERYTHING on the car is perfect. After looking at so many dogs, I was able to spot this gem right away (non-mechanic here).

I do have a question though. How can you tell when it needs a valve adjustment? Is that obvious or is that something that should be done every so many miles? I notice it shakes a little at idle. Is that normal for a diesel? It's not that bad. Everything else is like a brand new car and it has great pickup and drives beautifully down the road.

Thanks, Lance